Reconditioning alloy steel



Oct. 25, 1932. w. BJPLUMMER RECONDITIONING ALLOY STEEL Filed July 18, 1930 Extra, burners,

Inventor:

will/tomhpwmmwr Patented Oct. 25, 1932 UNITED STATES PATENT 0mm;

WILLIAM B. PLUMMER, OF CHICAGO, ILLINOIS, ASSIGNOR TO STANDARD OIL COMPANY (INDIANA), OF CHICAGO, ILLINOIS, A CORPORATION OF INDIANA BECONDITIONING ALLOY STEEL Application filed July 18,

This invention relates to a process and apparatus for reconditioning alloy steel and it pertains more particularly to the temperature resistant steels used in petroleum refinery apparatus,- such as hydrogenation units, cracking units, pipe stills, tubes, soaking drums, reaction chambers, etc.

The object of my invention is to minimize corrosion and prevent embrittlement of alloy steel used in petroleum refinery apparatus whereby replacement costs may be mmimized and safety may be insured. A further object is to operate hydrogenation units, cracking units, pipe stills, etc. indefinitely with a minimum amount of shut-down time for repair and replacement. A further object is to recondition alloy steel, preferably in situ, and to provide furnace structure whereby this can be accomplished. Other objects will be apparent from the following detailed'description.

I have discovered that if an alloy containing over .07% carbon is periodically heated to temperatures over about 1500 F., preferably of about 17 F. (in the absence of additional carbon) its life will be lengthened indefinitely, corrosion will'be minimized, and

embrittlement and formation of weak spots will be prevented. I believe that this is accomplished by eliminating segregation of carbon and/or carbides at grain boundaries.

The high temperatures apparently cause the carbon, which has slowly difiused from the grains, to be reabsorbed thereby so that there will be no weak spot due to accumulated carbon, chromium carbides or other intercrystal accretions.

The heating of tubes, soaking drums, stills, etc, to temperatures of the order of 1750- F. requires material modifications. to apparatus which is generally used in refineries. At these high temperatures the safe load is only a few hundred pounds per square inch and the tubes or other apparatus-must be supported thoroughly and at frequent intervals against sagging during the period of heating. In order that uniform temperatures may be attained and maintained throughout the entire volume of the furnace,

50 the heating must be uniform and it must be 1930. Serial No. 469,001.

initiated by slow fire; extra burners should be provided to insure proper heating of points farthest removed from the usual burn- V they must be modified accordingly, preferably by using fire brick throughout all sections wherein alloy tubes are used.

I prefer to utilize the heat in the exit gases during this high temperature heating period by means of suitable economizers, preheaters or exchangers; unless such means are em ployed it may be necessary to prevent excessive stack temperatures by introducing a large volume of air or inert gas directly into the top flue gases leaving the furnace.

The tubes, reaction chambers and other apparatus used in refining petroleum oils frequently become coated internally with deposits- 'of coke (carbon). This coke should be removed before the apparatus is reconditioned by high heat treatment because at such high temperatures additional carbon may be dissolved by the alloy which in turn will increase the rate of carbon and/or carbide'segregation thereafter. It is of importance that p the carbon -content of alloy-be maintained at a low figure. If carbon or coke has deposited on tube walls'it should be removed during the early stage of the high temperature treat mentby passing air through the tubes until carbondioxide no longer appears in the exit gas. Any means may be used, however, for removing the carbon from the apparatus prior to the reconditioning by heat treatment.

It is extremely important that the furnace structure be designed to withstand abnormal expansion and contraction due to the abnormal temperature changes. Tubes must not only be supported at more frequent intervals to' prevent sagging, but they must also be given more leeway for expansion. I prefer to use the so-called up-shot or De-. Florez type of heater wherein the tubes are vertically mounted in a circle around a central burner. Even this type of a still should be especially built to withstand higher temperatures and greater expansion than that heretofore encountered.

The invention will be more clearly understood from the following detailed description of preferred embodiments and from the accompanying drawing wherein:

Figure 1 is a transverse vertical section through a pipe still taken along the lines 1-1 of Figure 2.

Figure 2 is a vertical section through the same pipe still taken along thelines 2-2 of Figure 1, and

Figure 3 is a vertical section through an up-shot furnace of the DeFlorez type.

The pipe still or furnace structure does not differ from ordinary pipe still or furnace structure except that provision is made for heating the alloy steel tubes to higher temperatures. In other 'words, additional burners may be required, additional tube supports may be used, steel tubes may be protected by the addition of cold gases, and furnace temperatures may be tempered with recycled flue gases. Parts of the furnace which are exposed to unusually high temperatures are designed to withstand the additional expansion incident thereto. Otherwise the structure is not materially different from conventional furnace structures and it will therefore not'be described or shown in great detail.

Referring to Figure 1, pipe still 10 may consist of a steel frame lined with insulating.

material, the insulation of the upper part being preferably of fire brick. Heater tubes 11 are suspended from a roof by tube supports 12 and since these tubes are to be exposed to extremely high temperatures the tube supports are spaced close enough together to prevent tubes from sagging between supports. The ends of the tubes are accessible from openings 13 in the pipe still wall and when the return bends Mare removed therefrom carbon may be removed by scraping or by other conventional methods. Ordinarily the furnace is heated by burner 15, but to obtain the unusually high temperatures hereinafter described, I provide additional burners 16, particularly for heating remote parts of the alloy tubes. In order to temper the gases in the furnace, Imay recycle flue gas from the flue 17 through pipe 18, compressor 19 and pipe 20 back to the combustion chamber. A baflle wall 21 separates the combustion chamber from the convection chamber and in order to protect steel tubes 21 in the convection chamber I may introduce cold gas through pipe 22.

Referring to Figure 3, the furnace 23 is a steel cyclinder lined with insulating material tions of the tubes which are remote from the usual burner. I may temper the gases in the furnace by cycling flue gas through pipe 30, compressor 31 and pipe 32. In order to protect the steel tubes 33 in economizer section 34 I may introduce cold gases through pi e 35.

Fly invention may be applied to any high temperature alloy steel and as a specific example I may use a steel containing 18% chromium, 8% nickel, 15% carbon, small proportions of the usual impurities, etc., and the balance iron. This alloy is particularly well suited for withstanding high internal pressures and for resisting shock at elevated temperatures. If the tubes are used in a hydrogenation heater they may be operated at about 850 F. under a pressure of about 150-300 atmospheres. At frequent intervals it may be necessary to clean the apparatus and to remove deposited carbon. At such times (when tests or experience indicate that the steel has deteriorated) after the carbon has been removed I may slowly fire the furnace. and raise the'temperature of the tubes to about 1750 F., using auxiliary burners, recirculated hot gases, etc. for attaining and maintaining a uniform high temperature. The time re%1ired for the reconditioning varies with t 0 temperature employed; at 17 50 F. it is about 36 hours. At 1500 F. the time required is probably 45 or 50 hours, and higher temperatures will require less time.

At these high temperatures it appears that the carbon which is difiused from the crystals and which has segregated between the c stals is ice-dissolved so that a tenacious bon is once more obtained between these crystals.

While I believe that this is the explanation of my improved results I do not limit myself to any theory. Furthermore, I do not limit myself to the precise temperatures or other details hereinabove set forth except as de fined by the following claims.

The term carbon in the following claims includes carbon in the combined state as well as elemental carbon.

I claim:

1. In the refining of petroleum oils, the method of reconditioning deteriorated alloy steel oil-heating tubes which comprises cleaning the surface of the tubes to remove demethod of reconditioning posited carbon heating the tubes in situ to a temperature of over 1500 F. and maintaining the tubes at the elevated temperature for a suflicient period of time to restore the nonbrittle condition of the tubes.

2. The process of claim 1 wherein the period of time is more than thirty-six hours.

3. In the refining of petroleum oils, the

deteriorated oilheatin'g tubes composed o alloys containing more t an 6% nickel, more than 15% chromium, and more than 0.07% carbon which comprises cleaning the surfaces of the tubes to remove deposited carbon, heating the tubes in situ to a temperature of over 1500 F. and maintaining the tubes at the elevated temperature for a suflicient period of time to restore the non-brittle condition of thegtubes.

4; The combination of claim 3 wherein the period of time is more than thirty-six hours. Signed this 14th day of July, 1930, at Chicage, in the county of Cook, State of Illinois.

. PLUMMER. 

